The present invention relates to aircraft capable of vertical and short take-off and landing and, more particularly, to aircraft capable of such flight through the use of fixed wing sets and rotor wings that can be selectively stopped to act as fixed wings.
Aircraft designed to allow vertical and short take-off and landing, hovering, full forward flight, and transitional flight have existed since about the middle of the twentieth century. These vehicles are often referred to as dual mode or V/STOL aircraft because of their vertical and/or short take-off and landing capabilities. Traditional V/STOL aircraft have been designed to carry relatively small payloads. Reliably carrying large loads, such as loads weighing more than about 2 tons, using V/STOL aircraft has traditionally been problematic due to vertical thrust and aircraft control limitations.
One method of providing vertical thrust to an aircraft is by using a single rotor wing mounted atop the aircraft. A rotor wing is a structure that can be selectively used as a rotor and as a fixed wing. To increase vertical thrust characteristics for accommodating heavier loads, some V/STOL aircraft designs include a second rotor wing atop the aircraft. Even with two rotor wings, however, transitioning from vertical flight to forward flight while carrying heavy loads can prove problematic due to insufficient pitch control. A fixed wing set located about halfway along the length of the fuselage, i.e., in the region of a cargo bay, may provide lift and some pitch control, but it does not contribute enough pitch control for tandem rotor wing aircraft to simultaneously slow and stop both rotor wings while carrying a heavy load. Thus, when transitioning from vertical to forward flight, the rotor wings of tandem rotor heavy lift aircraft cannot be stopped simultaneously because one rotor is needed to provide pitch control while the other rotor is being stopped.
Another problem of traditional tandem rotor wing aircraft is a tendency for the blades of overlapping rotor wings to contact. The blade contact problem is often increased for heavy lift aircraft because the increased forces encountered by the blades cause the blades of the respective rotor wings to deflect by larger amounts from designated planes of rotation and into the paths of each other.